System and method for authenticated and privacy preserving biometric identification systems

ABSTRACT

A system and method for the identification of users and objects using biometric techniques is disclosed. This invention describes a biometric based identification and authorization systems which do not require the incorporation of an on-line database of stored complete biometrics for the security infrastructure. In order to remove the connectivity requirements, an off-line biometric system is achieved by incorporating an identity verification template (IVT) on a storage device/token (e g, magnetic strip or smart-card) during the user&#39;s registration which provides for a reliable storage medium; however, there are no security requirements required of the token even to protect the privacy of the stored biometric. The IVT does not contain complete information of the user&#39;s biometric but allows for the verification of the user when that user later provides a biometric reading. To deal with errors that may be introduced into later scans of the biometric (for example at the time of verification) error correcting techniques, well known in the art of communication and error control systems, are incorporated into the system. The system is also usable in the online model. Moreover, it may also be used to enable cryptographic operations by being used to partially compose or encrypt private keys for cryptographic operation.

CROSS REFERENCES TO RELATED APPLICATIONS

This application is a Continuation of U.S. Patent Application no.09/303,053 filed Apr. 30, 1999, which issued as U.S. Pat. No. 7,711,152,on May 4, 2010, the contents of all of which are incorporated byreference.

FIELD OF THE INVENTION

The present invention is related to the field of identification(authorization), and more specifically to the identification(authorization) of users/objects, and sets of users/objects throughpattern recognition and identification. These patterns may be derivedfrom measurements of features of the human body. These patterns may alsobe derived from measurements of physical features of an object or frompatterns applied to an object such as on a label. Patterns derived fromphysical features (such as fingerprints or iris patterns) or emissions(such as voices) of the human body are referred to herein as“biometrics”. The present invention finds particular utility inidentification of objects and biometric identification of humans.

DISCUSSION OF THE RELATED ART

In some conventionally available biometric identification systems, ascan of the iris is used as the biometric identifier. In theseconventional systems, a database of the iris scans of individuals ismaintained, either on-line or in a portable token such as a card with amagnetic strip on it. When the user desires access to a secure area, acurrent iris scan is taken and this current scan is compared to the scanstored on the token or in the database. If the two scans match withinsome predetermined acceptable limit, the individual is consideredauthorized and allowed to proceed into the secure area. One problem withsuch a system is that the individual's actual iris scan is stored in theon-line database or on the token. If the token is stolen or if thesecurity of the on-line database is compromised, an individual's irisscan is no longer protected. From a privacy point of view, an iris scanof an individual can reveal certain aspects of the individual's health.Therefore, if someone unauthorized obtains an individual's iris scan,private medical information may become available to unauthorized people.

SUMMARY OF THE INVENTION

The present invention overcomes the deficiency of the prior art byproviding a pattern recognition and identification system that does notrequire storage of the pattern to be identified in either an on-linedatabase or offline on a token. Since the actual pattern or biometricidentifier is not explicitly stored, theft of the stored informationdoes not compromise an individual's privacy or reveal private aspects ofan individual's health. In the case of pattern recognition withinanimate objects, since the actual identifying pattern is not stored,opportunities for theft of objects or replacement of objects withfraudulent ones are greatly reduced.

In accordance with one aspect of the present invention, a method isprovided for generating an identification and verification templatecomprising the steps of obtaining a user biometric and generating adependency vector for the user biometric such that the template is boundcryptographically to the user.

In accordance with another aspect of the invention, a method is providedfor uniquely identifying a user via biometric analysis comprising thesteps of acquiring an input comprising a User Biometric from a reader(UB), an input comprising an identity verification template (IVT) from atoken or card, and performing a validation protocol given as input theuser's biometric (UB) and the IVT, whereby a decision value is computedgiven authorization information and possibly other information.

In accordance with another aspect of the invention, a method of securepattern recognition is provided comprising the steps of acquiring afirst pattern, combining the pattern with authenticating information,encrypting the combination of the pattern and the authenticatinginformation to provide a template, acquiring a second pattern, andprocessing the second pattern and the template to determine if the firstpattern and the second pattern are the same.

In accordance with another aspect of the invention, a method ofproviding an individual verification template comprises the steps ofacquiring a biometric pattern from an individual and cryptographicallycombining the biometric pattern with authenticating information toprovide the individual verification template.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1. is a diagram depicting the authorization's officer input intothe storage device.

FIG. 2. is a diagram depicting the identification of a user to aapplication.

FIG. 3. is a diagram depicting encrypting a template multiple timesunder different keys.

DETAILED DESCRIPTION

The present invention will now be explained in detail with reference toits use in secure biometric identification of a human. However, theinvention is applicable to a wide range of pattern identificationapplications and therefore the following description should not beconsidered as limiting. The invention may be used in any applicationrequiring secure pattern recognition.

Systems for acquisition, storage, and processing of biometrics are knownin the art and described in some of the documents which are incorporatedby reference into the present application. For simplicity, such systemsare not described further in the present application.

In developing secure applications and systems, designers oftenincorporate secure user identification in the design specification.Secure identification schemes are becoming increasingly important, asmore security applications require identification based on physicalcharacteristics rather than solely on a user's knowledge of a secretcryptographic key or password. The increased interest in suchapplications, ranging from door access to electronic commerceapplications, has led to an increased interest in methods for secure andaccurate identification of individuals as well as machines and objects.Some of these systems of identification use measurable biologicalfeatures, biometrics, which can be readily measured at the point ofapplication.

It is desirable, though not required, that such measurements benon-invasive and simple to perform. One biometric identification systemthat is in the art is the iris scan [Bouchier96, Flom, F2, Holmes90,Daugman1, Daugman2, Daugman3, Williams96] though others are know in theart such as retinal, fingerprint, handwriting, face recognition, voice,DNA etc. Moreover, non-biological objects may also be identified usingthe biometric technology and we use the term biometric in this aspecteven though these may not be biological.

The human iris is the colorful doughnut-shaped organ surrounding thepupil, as distinguished from the retina which is the hemispherical organbehind the cornea, lens, iris and pupil. The iris has highly detailedtexture and is unique for each individual, differing between identicaltwins and between left and right eyes of the same individual. It hasbeen determined that the iris imparts the same or better singularity toindividuals as the fingerprint. It is known in the art how to acquire aniris scan of an individual. For instance methods and apparatus describedin [Daugman1] may be used.

Our working example is based on iris recognition systems. In an irisrecognition system a user presents himself/herself to the system, whichthen acquires a digital or video image[s] of the eye[s]. The systemperforms image analysis to determine if an iris is visible, the degreeof occlusion of the iris by the eyelid, and the degree of spectralreflection; it also assesses the quality of the focus and locates theiris. The system adjusts for pupillary constriction, overall image size,head tilt and cyclovergence of the eye. The system then proceeds tocompute the encoding (scan) for the iris. It is known in the art [Flom,Daugman1, Dauman2, Daugman3] how to generate a digital pattern of theiris using techniques from signal process such as digital filtering andconvolution.

In one mechanism for an iris recognition, a scan (pattern) of the user'sbiometric is stored (and registered) during a user registration. This isthe registered iris scan or iris code. During identification, a newacquired pattern is compared to a previously registered iris scan.Similar techniques may be used for biometric identification systemswhich are not based on the iris.

A biometric identification system that stores the biometric in a centraldatabase or provides the user's biometric in an unsecured manner may notbe acceptable to a user, because a user's biometric could be used forunacceptable purposes if the biometric is obtained by an unauthorizedindividual. A user's biometric can provide information which a user maynot want provided readily. For instance, a finger print reading can beused for law enforcement purposes and an eye scan (retinal or iris) maybe able to detect medical conditions.

What does not exist in the art are methods for protecting a user'sbiometric on an insecure device or secure use of the biometric in anonline system. Such protection may be beneficial if the storage deviceholding the identity verification template (IVT) is lost or stolen. Whatare needed are mechanisms specifically designed to reduce the chances ofdisclosure of a user's private biometric data without requiring hardwaretokens containing mechanisms to hide stored information. An importantsecurity system to consider is the case where neither the user nor thereader maintains private decryption keys, because it is a scalablesolution when the user must have authorization amongst multiple readersand when password protection is inappropriate.

One of the difficulties of prior art is that prior methods are based ona compare operation of two like, or similar, iris scans. That is, duringregistration a scan of the iris is generated and stored. During the useridentification process (sometimes called the verification process) a newscan is generated by obtaining a new reading from the user. The twoscans, the prior one from registration and new reading just preformed,are compared. This, however, requires storage of iris scan informationin a form which essentially allows reproduction of all the informationfrom the original (registered) scan. Note, however, this is not adesirable property if one wants to protect the privacy of the user'sbiometric as described earlier.

Conventional on-line applications secured through the use of biometricauthentication typically are based on a push or pull model. In bothmodels, the first step is a user initialization, which occurs when theuser's biometric (UB), and other information, is registered with theon-line server. After initialization, when a biometric identification ofa user is required, a biometric authorization process is performed. Atthis time the user's biometric is read by a reader. In the push model,the reader transmits (preferably via a private channel) the reading tothe on-line server; the on-line server then verifies the validity of thereading based on the user's biometric in the server's database; andfinally the server sends an authenticated acceptance or rejectionmessage back to the reader. In the pull model, the reader requests thebiometric from the server, and the reader performs the verificationsteps after receiving the biometric over an authenticated and,preferably, private Channel from the server.

In both cases, an authenticated channel is preferred for somecommunications between the on-line database and the reader. Theauthentication can also provide for a binding of a user's biometric withsome form of authorization, as established by trust relationshipsbetween the reader and the on-line database. The online model is notalways practical in mobile environments, such as military applications,and are often cost prohibitive since they require expensive wiring forconnectivity or costly wireless devices.

Within this disclosure, the term “on-line” is meant to refer to a systemin which biometric identification information (or pattern recognitioninformation in the case of inanimate objects) is stored on a server orsome other central repository of information used to identify more thanone individual. For example, the central repository could containinformation needed to identify all employees of a company. Within thisdisclosure, the term “off-line” is meant to refer to a system whichcontains no stored remote biometric identification information (orpattern recognition information in the case of inanimate objects) isused during identification thereby not requiring connectivity to aremote server.

It should be noted that an off-line system which protects privacy isalso applicable to on-line systems where information is stored in anon-line database instead of on storage cards. By using such a system inan on-line environment as disclosed in this invention, one is able toreduce the security requirements imposed on the database. The embodimentpresents techniques which prevent the database manager from reading abiometric directly from the database or archives.

We also note that designers of secure systems are often hampered by thelack of mechanisms to satisfy the various requirements of a secure keymanagement infrastructure. This infrastructure may have to deal withgeneration of both public and private keys, authenticated disseminationof keys, and the storage of keys, as well as other concerns such asmaintaining privacy of users and trusted circulation of userauthorizations.

The security of this infrastructure is often hindered by insufficientmechanisms to secure private keys for users. Currently passwordencryption techniques are used in the art but these are based on thesecurity of the user memorizing a sufficiently large and secret value.What is not known in the art is how to incorporate additional randomnessfrom the private biometric into a password encryption.

When one assumes that a user's biometric information has sufficientuncertainty, our technique also allows for the biometric to be used as aprivate key. Since there may not be sufficient entropy (i.e.,uncertainty) in a user's biometric, our system allows us to augmentpassword encryption with the entropy provided in a biometric. Biometricsystems based on a compare operation are not effective in providing thisform of service.

The invention deals with the use of basic cryptographic authenticationsystems and basic e or correcting mechanisms to generate a user identityverification template (IVT) that can be incorporated into a securityinfrastructure providing for user biometric identification. Theinvention involves mechanisms which provide for user initialization togenerate a user IVT for online and offline systems as well as abiometric authorization process. It further develops an IVT using errorencoding mechanisms (See [Berlekamp, PetersonWeldon,MacWilliamsSloane78] for known techniques in the art) that provide forthe correction of errors introduced into future readings of a user'sbiometric (UB).

It involves methods in which privacy of the user IVT is enhanced withand without cryptographic encryption to protect the information fromunauthorized entities. It further involves methods in which the IVT orother stored biometric info is a lossy (i.e., information losing) notrequire the use of a compare operation of the user's biometric acquiredat verification time with a biometric that was generated previouslyduring a user's registration and initialization as an authorized user.By using an operation different than a compare new scalability andsecurity features are incorporated into the design. It further involvesmechanisms which bind public and private user attributes to the user'sbiometric.

It further develops mechanisms in which biometrics provide an enabler tocryptographic function by deriving the secret key for the cryptographicfunction from the biometric information as well as other privateinformation such as PINS as well as other information.

However, even though the invention can be used in an offline embodimentit can be used in the online transformation of the UB. The inventiondescribes a biometric authentication process which does embodiment aswell. (See [Pare] for a model that this invention works with). Ourembodiment is not limited to the off-line case.

A user in this invention is an entity usually associated with some roleor capability though it does not necessarily have such associations. Itis generally defined as an individual or set of individuals with somephysical, preferably unique and hard to reproduce, characteristics. Someexamples are DNA, fingerprints, retinal, voice, iris, brain waves,handwriting, facial, and hand geometry. Our working example is anindividual with a unique iris in which there will be a linking betweenan iris scan (also referred to in the art as an iris code) to thatindividual.

However, the invention is not limited specifically to individuals oriris scans, and may work with other types of biometrics. It allows forsets of individuals (e.g., via scans of the iris of several individuals)and other non-human objects.

For instance, it may be a vehicle, smartcard or other object in whichsome component is sufficiently unique, is non-reproducible, and islinked to the object and can be read for secure identification. A userbiometric also may be identified by several unique factors (e.g., aniris and a finger). It may be a combination of biological andnon-biological components such as a unique iris and a specific tokenwith a unique tag. It should be noted that each component may not beunique by itself but have uniqueness as a combination such as two ormore biometrics (which by themselves are not unique) but define a uniqueentity (User Biometric UB) when all are taken into consideration. (Byuniqueness generally we mean it will be different than any otherbiometric with high probability). A user's biometric may also be aportion of the component acquired (e.g., it may be only a portion of anindividual's iris).

Users may have attributes associated with them. Some examples areprivileges and role (title, position, etc.) of the individual, physicalcharacteristics of the individual, etc. Some important attributes thatare considered here are role and capability. The notions of roles andcapabilities are known in the art of computer security, data securityand network security (e.g., [Denning]). Capabilities which describeauthorizations are of particular interest because they may be related tothe biometric based application.

For instance, the biometric based application may be a door access andthe capability assigned to a particular user is access to particularrooms. We note that user attributes may be directly or indirectlyrelated to the user. An attribute may be something like a user's publickey which is used for some public key application, or an access controllist. Indirect attributes may be a description of another object such asa token or other physical device that the user may need foridentification (i.e., a necessary prerequisite to obtain a capability isa valid scan and a specific token). The token may be made unique byembedding a physical characteristic (see [Nacaache]).

Another attribute of a token may be private memory it holds. It may bethat there is a binding of a public vector related to privateinformation stored in a token. Then using a zero-knowledge cryptographictechnique or authentication techniques, the token can prove knowledge ofthe private information. These techniques for proving knowledge ofsecret information are known in the art of cryptography (See [Shamir86,Menezes] for examples).

The authorization officer's role is to certify (e.g., authenticate orsign) a binding between a user's biometric and some other attributes ofthe user. (See FIG. 1 in which the security officer takes as input theinitial user biometric template, user attributes and user authorizationsand stores the necessary information on a storage device). Theauthorization officer is thereby the trusted third party attesting tothe authenticity of the user is biometric as well as to other userattributes. The authorization officer plays a role that is similar tothe Certification Authority (CA) in a public key hierarchy (see [x509]),except that the authorization officer binds biometrics to userattributes, while a CA generally binds a public key to user attributes.

It should be noted that the authorization officer(s) may be one or moreentities and may be incorporated into some infrastructure as is known inthe art. Some example are hierarchical but our invention is not limitedto such structure. In the system described in this embodiment, thefunction, Sig(input), is a cryptographic authentication function whichlinks the authentication of input to the authorization officer.

That is, in a public key authentication Sig(input) is the signature ofinput by the authorization officer and in a private key authenticationsystem it is the authenticator using a private key known by theauthorization officer and the reader. Without loss of generality, weassume throughout that Sig is a public key function and thoseknowledgeable in cryptographic system design will be able to use knownmechanisms to use other types of authentication functions and systems.

In an off-line system, the biometric authorization process cannot have adirect (on-line) information retrieval mechanism. We should note,however, that as with any off-line identification system, immediaterevocation of user privileges is not possible. This limitation must betaken into consideration by the system designer during the developmentof the security architecture. For instance, a bad list may be kept incache and the local storage may be periodically refreshed. Suchmechanisms are known in the security architecture state of the art andare known by those knowledgeable in the field. We now discuss thework-flow in the off-line model.

User Initialization (registration): The secure authorization officertakes as input an initial biometric reading, called the user biometric(UB), the authorization information defining the set of privilegesgranted to the user by the authorization officer, and other userattributes. An output storage device such as a magnetic strip card(diskette, smartcard, etc.) is encoded with information whichestablishes a binding between a user's biometrics (and, possibly, otheruser attributes) and the user's authorization granted by theauthorization officer. (See FIG. 1). Other information and a bindingsmay also be included.

Biometric Authorization Process: During a secure application a readertakes as input the user's storage device (token) and acquires the user'sbiometric. Given this information the user's attributes can be obtainedand linked to the authorization officer. Of particular interest is thatcapabilities for the secure application may need such information todetermine how the application should function if the user is identified.The information from the card may now be transmitted to the secureapplication or the reader informs the application of the validity(acceptability) of the user.

See FIG. 2 which depicts the biometric authorization process. In thefigure the reader is secure and the communication between reader andapplication is secure (i.e., authenticated and/or private). The securityof the channel may also be protected by means other than cryptographictechniques, such as physical protections.

Note that the storage device can be replaced by an authenticatedtransmission link to the authorization officer (or its database) in theon-line system. The authentication (signature) in an online system doesnot need to be stored but rather created at time of request. Themechanisms described in this embodiment allow for online biometricidentification systems.

Certain principles can be incorporated into the system disclosed in thisembodiment: There is a binding between a user's biometric and a trustedauthorization officer. There is a need for a scalable solution whenprivacy of a user's biometric must be protected in case a storage deviceis lost or stolen. The primary scalability issues are who must storeprivate keys and how much storage must be provided on the cards. One cannote several off-line, as well as online, security architectures bydetermining who, if anyone, must hold a private key.

Let us describe some models below where we discuss privacy of a user'sbiometric but similar techniques can be used to hide other information:

PRIVATE KEY IN READER: If a reader has a private key to decryptbiometric information encrypted by the authorization officer (and storedon the card), then there will be no leakage of biometric informationwhen a card is lost or stolen. However, such a system is not scalable ifthe memory device has low storage capability and the application'sarchitecture requires multiple readers (each with its own private key),because a separate encryption of the biometric is required for eachreader. (See FIG. 3 which depicts a magnetic strip with limited memorystoring multiple encryptions of the same identity verification templateIVT but encrypted with different keys).

This technique, however, can be effective if there are few readers inthe architecture. To be effective, this approach requires that thereaders provide some form of protection for the reader's private key(e.g., FIPS PUB 140-1 standards), because if the private key is stolenfrom the device, the adversary is able to read the biometric from anyuser's storage device.

SECURE TOKEN: A token with (direct or indirect) computational capabilitymay store the private information in a secure place in its memory.Preferably this memory is destroyed if tampered by unauthorizedentities. The token has a capability to verify the reader through anentity authentication technique. Upon verification, the privateinformation is transmitted to the reader.

Other mechanisms are possible. An authenticated channel may beestablished between the token and the reader using techniques known inthe art of cryptography and data security and the information istransmitted via that channel. These and other techniques are known inthe art of cryptography and data security (See [Schneier, Menezes]).

PASSWORD-PROTECTION: Password protection can hide information stored ona card (such as the user's biometric) if the password has sufficiententropy. This approach is a scalable solution (e.g., using passwordencryption [PKCS5] to encrypt the biometric info with a user memorizedpassword), if revealing a password to a reader is considered safe andthe readers have a user password input mechanism. Generally, passwordprotection is considered insufficient, since 10 it usually has lowentropy and is therefore easily guessed. As a result FIP PUB 190recommends the combination of PIN/password and a token for userauthentication when feasible [FIPS 190].

However, it should be noted that though ineffective in some applicationsit is useful in some. Especially since it is a low cost mechanism. Thismechanism for instance can be incorporated into a public key certificatemechanism in which the biometric is password protected in thecertificate. The use of password protection to protect biometricinformation or to protect private information in a certificate isdisclosed here.

NO KEYS OR PASSWORDS: Potentially, this is the most scalable approachwith minimal system component requirements for an off-line system. Suchsystems, as will be shown, are possible when the entropy in a biometricis large enough. Except for the secure token model, all the aboverequire no special security requirements from the token. It justrequires that the token has a storage capability.

It should be noted that the off-line systems we shall discuss are alsoapplicable to on-line systems where information is stored in an on-linedatabase instead of on storage cards. By using the offline mechanismsdescribed in this embodiment in an on-line environment, one is able toreduce the security requirements imposed on the database, where privacyrestrictions on the information exit.

3.1 Identification Scheme

An (N,K,D) code is set up such that it can remove enough errors to allowthe system to recognize the legitimate user of the card but not someoneelse, i.e. bounded distance decoding. An (N, K, D) code is a code ofN-bit codewords (vectors) where K is the number of information digitsand D is the minimum distance of code. It should be noted that an errorcorrecting code ECC with rate K/N can correct T=(D−1)/2 errors. To allowfor error correction of a biometric, we encode a K bit biometric into anN bit code vector, with N-K redundant (or check) digits. These are thedependency bits mentioned above.

We also use majority decoding which is known in the art. Letvec{c_(i)}=c_(i),1, ∥c_(i),2, ∥ . . . ˜c_(i), n, be n-bit code vectors.As an example of majority decoding odd m vectors vec{c_(i)}, a majoritydecoder computes vector Codeword=C₁∥C₂∥ . . . Cn, where Cj=majority (c₁,j, . . . c_(m), j), i.e., Cj is the majority of 0's or 1's of bit j fromeach of the vectors (“∥” is an OR operator). We shall use majoritydecoding primarily to get the best biometric reading possible, thusreducing the Hamming distance between successive final readingsCodeword.

The description of an (N, K, D) error correcting code, preferably, withrate K/N>1/2, (using bound distance decoding of up to (D−1)/2 errors),is provided to the authorization officer and biometric readers. With[Daugman1, Daugman2, Daugman3], it should be noted that the averageHamming distance between unrelated scans is about 47 percent (i.e.,about 962 out of 2048 bits), making a bogus scan too far from a targetedscan on the average. Even if one considers the overlap in thedistribution of the Hamming distances of the same subject (average ofabout 10 percent Hamming distance), and the distribution of Hammingdistances of unrelated scans, the overlap occurs at around 21 percent,at negligible probabilities.

The technique of majority decoding that we introduce here ensures thateach biometric vector, be that bogus or valid, will tend toward an“average” vector for the individual being scanned, thus moving theHamming distance of a bogus scan (from a valid scan) closer to thestatistical average of about 47 percent. These value are exemplary andare not limiting.

Our invention is not limited to error correcting codes which use abinary alphabet. For instance, p-ary codes are known and our inventionallows for systems using such mechanisms. In these cases hamming weightis different and such mechanisms can be modified to incorporate suchcodes. We also are not limited to linear codes though these are commonlyused and bounded distance decoding is preferable but not required.

Let us now describe a biometric identification system. A feature of theinvention is that information that binds the user to the biometric isenabled by the authorization officer.

-   -   System Setup: The authorization officer generates its public and        private key signature pair, and then disseminates its public key        to the biometric readers. The system also sets up an algebraic        (N,K,D) code.    -   User Initialization: To register, IM biometric scans of length K        are generated from the user. These IM vectors are put through a        majority decoder to obtain the user's K bit biometric Biodigits.        These scans (vectors) are similar to the iris code used in        [Flom, Daugman1, Daugman2, Daugman3] and in fact the same        process to generate an iris scan may be used. Techniques such as        those presented by [Flom, Daugman1, Daugman2, Daugman3] may be        used to generate vectors of K bits (also called an iris code).        Given the K information bits Biodigits a codeword        IC—Biodigits∥Checkdigits formed where Checkdigits are the check        bits in the (N,K,D) code defined in system setup. The check        digits are one form of the “dependency vector” which will be        computed for the biometric.

The following four items may go on the card:

-   -   Name of the individual, NAME.    -   Other public attributes ATT, such as the issuing center and a        user's access control list.    -   The check digits Checkdigits, of the biometric.    -   Sig(Hash(NAME, ATT, Biodigits∥Checkdigits)) where Sig(x) denotes        the authorization officer's signature of x, and Hash(.) is a        partial information hiding hash function [canetti] (e.g.,        Sig(Hash(.)) is a content-hiding signature) or a random oracle        (See [BR]).    -   Biometric authorization process (verification): When a user        presents a card, VM biometric readings are independently        generated for the user. Each reading results in a biometric        vector, also called an iris code. These VM vectors are put        through majority decoding to obtain the user's K bit biometric        (UB) VBiodigits. Error correction is performed on the codeword        VC=VBiodigits∥Checkdigits to obtain the corrected biometric        Nbiodigits. The signature Sig(Hash(NAME, ATT,        NBiodigits∥Checkdigits)) is then verified against the data from        the IVT on the token (card). Successful signature verification        implies the user passed the identification step.

Other information may be incorporated and signed (authenticated). Theremay be checkdigits for other user characteristics (e.g., retinal, voice,etc.), from other individuals (e.g., scans from other individuals (e.g.,if two people are needed for authorization then both biometricscheckdigits for both individuals can be incorporated) Similarly,biometrics for inanimate objects may be incorporated. Also it should benoted other biometric templates such as biometric codes, rather thancheck digits, may be incorporated (e.g., biometric systems which use acompare). It is not the intent of this example that only checkdigits beused or limiting to one biometric characteristic.

The above process is exemplary. Instead of a signature one may use aprivate key authentication systems (See [Schneier]) and as describedearlier a different type of error correcting mechanism. Theincorporation of an information hiding hash (or random oracle) is forthe purpose of protecting the private input (e.g., Biodigits) to thesignature function from being leaked since signature may leak theirinputs. When this property is not needed then such additional complexityof incorporating the hash function (random oracle) is not necessary. Ifcryptographic authentication is not needed then Sig field may be omittedor preferably a hash (unkeyed) of the values may be used instead.

Moreover, the authentication field may be embedded into the checkdigits. It should also be noted that majority decoding may not benecessary especially if one can obtain an error free reading. Observethat the same technique can be used for online systems. Instead ofputting the information on a card this information may be transmitted atthe time the biometric authorization process needs the information.Observe using similar techniques both push and pull models are possible.

The public attributes in the above may also include ciphertext ofencrypted information which is private. Such information is encryptedsuch that the reader can obtain the decrypted information. Throughoutthis embodiment we will assume that the field ATT contains publicinformation and ciphertext of private information.

3.2 Biometrics as an Enabler

If the biometric has sufficient entropy, than the biometric itself canbe used as a key. In fact, the biometric becomes a key for encryptingother private keys and private information. Thus, biometrics can be anenabler of cryptographic functions, if there exists sufficient entropyin the biometrics.

We show how to enable cryptographic applications through biometrics,since biometrics can hide private information such as keys. It may beworthwhile to encrypt other valuable information, such as cryptographickeys (Keys) such as the user's application keys for the application,private attributes (Private) including private access control lists, andother biometric information (Bio) including physical descriptions (e.g.,Brown hair, Hazel eyes, 5′11″, 200 lbs.).

There, of course, is concern that a biometric is a lifetime key thatcannot be revoked easily. Therefore, biometrics may be augmented usingpasswords, PINS, etc., with biometric entropy, in essence takingmultiple sources with weak entropy to produce a key with a largerentropy. We included a PIN in this protocol to allow the user to addentropy into the final key. This addition is especially important whenthe privacy assumption may be in question.

Now, instead of a signature as in the previous protocol, the followingencryption is encoded for each application A (where KA is applicationA's private key and PINA is the user's PIN for application A). Note thatthe signature does not need to be inside the encryption but it ispreferred for security reasons.

New item enc_(A)=ENC([Hash(K_(A), PIN_(A), Biodigits)], (Keys,PrivateBio,Sig(msg)), where Sig(msg)=Sig(NAME, ATT, Keys, PrivateBio,Hash(Biodigits∥Checkdigits))) and [Hash(K_(A), PIN_(A), Biodigits] is anencryption key.

Biometric authorization process (verification): When a user presents acard, VM biometric readings are independently generated for the user.Each reading results in a biometric vector, also called an iris code.These VM vectors are put through majority decoding to obtain the user'sK bit biometric (UB) VBiodigits. Additional error correction isperformed on codeword VB=VBiodigits∥CheckDigits to obtain the correctedbiometric NBiodigits.

The system now computes key Hash (K_(A), PIN_(A), NBioDigits) which cannow be used to decrypt enc_(A). The signature may now be verified.Successful signature verification implies the user passed theidentification step. A universal one way hash function [NY] as known inthe art of cryptography is the preferable choice for the Hash function.

There are other techniques known in the art for composing a key, withthe pin and the biometric vector BioDigits, for instance, it can becarried out by a universal one way function keyed by K_(A) with inputbeing the PIN_(A) and BioDigits.

Our example above is private key based however the technique is notlimited to such encryption. The encryption can be public key based usingthe public key rather than the private key. Also observe that the key(i.e., Hash (K_(A), PIN_(A), NbioDigits)) generated with the biometricdoes not need to be used for encryption but it may be used directly forother purposes (as the application's key). The intent of the encryptionin the preferred description is exemplary but it is very useful inparticular when an application's keys must have special form such as anRSA key rather than being random.

3.3 Adding Private Attributes

The system includes public attributes as components incorporated intothe stored memory device. However, private attributes can also beincorporated as well. Private information may be encrypted in a mannerin which the reader's private decryption key can be used to decrypt theinformation. Of course this private information, or the ciphertext,should also be authenticated with the other information on the card.This however is not always a scalable solution. One can also usepassword encryption in which the user must supply a password which isused to decrypt the information.

Another mechanism is using the biometric as an enabler mechanism. Theprivate information is incorporated in the same manner as thePrivateBio.

3.4 Algorithmic Implementations

For (N,D,K) error correcting codes BCH codes, which are well known inthe art of error correcting codes theory and information theory, can beused With BCH codes one can generate codes for a suitable length. See[ShuLin, Rhee, BerleKamp, MacWilliamsSloane78, PetersonWeldon] fordiscussions on the implementation of BCH codes. We also allow, but notrequire, for the incorporation of bounded distance decoding whichenforces that only a limited number of changes (modifications) areallowed to be made during decoding, This may be done in numerous ways,the preferred method is that during decoding when determiningerror-locations only an allowed number of changes are permitted. Thismay be done in the same process as [Rhee Section 7.5.2] which describesthe “computation of error-location number” in the decoding step bycomputing reciprocal of the roots of the error locator polynomial.

Our invention is not limited to binary codes or BCH. Many other types oferror correcting systems will work. The primary process includes a lossytransformation of the biometric and or other data during a registrationprocess resulting in data we call the dependency data, or vector. Thedependency vector is stored with possibly other dependent information(e.g., authenticators of stored information, public values, etc.). At alater time verification is performed by acquiring the informationgenerated at registration as well as a newly acquired biometric scan andother information, thereby validating the link between the biometric andthe information provided at registration.

In one application of this process, registration includes a lossytransformation of the biometric and cryptographic authentication of thebiometric. Instead of an authenticator, a hash may be used in some casesor it may even be omitted. The link may also express other relationshipssuch as a third party (e.g., a CA) validating the relationship betweenthe biometric and dependency data information digits. An example is theinformation digits of a BCH codes.

Other functions are non-linear functions of the information digits arealso possible as well. These functions may also come from those whichcome from the art of error correcting codes. Furthermore, the dependencydigits can be linear or non-linear functions of the biometric and otherdata as well. In addition with error correcting codes, it is possible toshorten the check digits, that is remove part of the dependency vector(check digits).

Such schemes are known in the art [Berlekamp, DavidaReddy72] aspuncturing an error correcting code and can be used in schemes where oneor more part of the check digits are used in one step of the decodingprocess and the remainder part[s] of check digits are used in theremainder of the decoding process.

We shall use as an example the biometric cited in [Daugman2 andDaugman3], the iris code of length 2048. For this iris code, theexpected number of errors between successive readings is about 10percent, i.e. about 205 errors. With majority decoding, which we use, wecan, for example, use 11 readings for an individual and reduce theeffective distance between successive final user biometrics to about 1on the average. This reduces the demand on the error correcting code.Assuming that at most 3 errors will be present, then a shortened BCHcode (See ShuLin, Peterson and Weldon, Rhee) of length 2048+36 bits(i.e., 36 check digits) can correct 3 errors in the final user biometricacquired at verification time. This is an example.

Readings of the biometric are subject to technology changes, and for theiris code or other biometrics the actual errors between successivereadings may vary. It is recommended that the total number of checkdigits (the dependent vector), as a percent of the length of errorcorrecting code, N, be less than 50 percent. For example, one can setthe recommended number of check digits to be no more than 35 percent ofthe code length N.

There are many hash functions which have been developed for the use incryptographic and other applications (See [Menesez] for variousimplementations of hash functions) with the most commonly used hashfunctions for cryptographic applications today are SHA-1 [FIPS 180-1]and MD-5 [MD5]. Both of these are usable in this invention but theinvention is not limited to only these. It should be noted thatcryptographically secure hash functions are used for digital signaturealgorithms as well. In the system, we can also incorporate both publicand private key encryption. For private key encryption, DES is thepreferred mode of operation for this invention (See [FIPS 46-2] forstandards on this implementation).

Other private key systems work also, including a proposed new governmentstandard AES of key length larger than that of DES. In our system withDES, when [Hash (K A, PINA, Biodigits] is used as the encryption(similarly, decryption) key then only the lower order 56 bits are used.However other set of bits may be used as well. Moreover, other DES modesof operation may be used such as those described in [FIPS 81]. Forpublic key encryption, our recommended algorithm is RSA but others maybe used such as the El Gamal encryption (See [Menesez] forimplementations).

There may also be a combination of both public and private keytechnologies in order to allow for efficient implementations. In suchschemes, a session key is transferred via public key mechanisms such asRSA encryption or a Diffie-Hellman Key exchange. The session key is thenused with a private key encryption mechanism to encrypt the data (See[PEM] for an example).

For the public key signature the preferred implementation is the digitalsignature algorithm (DSA) [FIPS 186]. Other systems may be used as wellsuch as RSA signatures such as is used in [PEM]. Our system is notlimited to the type of digital signature algorithm that is used.Depending on the security model, private key authentication may be usedinstead though this may not allow for scalable operations.

REFERENCES

Each of the following publications is incorporated herein by reference.

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[FIPS 46] FIPS 46, “Data Encryption Standard”. Federal InformationProcessing Publication46, US Department of Commerce/N.I.S.T., Apr. 17,1977. (revised as FIPS 46-1, 1988, FIPS 46-2, 1993).

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encryption and authentication procedures”, Internet Request for Comment1421, J. Linn, February 1993 (See also RFC 1422, RFC 1423, RFC 1424).

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Although not described in detail, one skilled in the art would be ableto implement the present invention by using readily available hardwareand software techniques based on the teachings set forth herein and thereferences referred to and incorporated into this disclosure.

Having thus described at least one illustrative embodiment of theinvention, various alterations, modifications, and improvements willreadily occur to those skilled in the art. Such alterations,modifications, and improvements are intended to be within the spirit andscope of the invention.

Accordingly, the foregoing description is by way of example only and isnot intended as limiting. The invention is limited only as defined inthe following claims and the equivalents thereto.

1. A method for uniquely identifying a human or non-human object viabiometric analysis, comprising: generating a first user biometric (UB)from a plurality of data bits of information stored on a first server onan biometric system including one or more servers and one or morebiometric scanners used to collect physical biometric information from ahuman or non-human object, wherein the physical biometric informationcollected from the human or non-human object is stored as the pluralityof data bits of information on the one or more servers on the biometricsystem; encoding authorization information defining a set of privilegespreviously granted to the human or non-human objects for a securityinfrastructure into the generated first UB via an application;generating an Identification and Verification Template (IVT) from thegenerated first UB via the application; generating a dependency vectorfrom the IVT via the application, wherein the dependency vector isgenerated with a lossy transformation of information stored in thegenerated first UB, wherein the IVT does not include completeinformation from the generated first UB but does allow for verificationof the human or non-human object when the dependency vector generatedfrom the IVT is accessed a later time.
 2. The method of claim 1, whereinthe physical biometric information includes an iris scan or a portion ofan iris scan of the human.
 3. The method of claim 1, further comprising:storing the generated first UB or generated IVT on an off-line biometricstorage device.
 4. The method of claim 3 wherein the off-line biometricstorage device includes a magnetic strip card or smart card.
 5. Themethod of claim 1 wherein the one or more servers include on-lineservers or off-line servers.
 6. The method of claim 1 furthercomprising: generating a second user biometric (UB) for the human ornon-human object via the first server on the biometric system;retrieving the dependency vector previously generated from the IVTgenerated from the generated first UB via the application on the firstserver on the biometric system; and verifying an identify the human ornon-human object using the generated second UB and the retrieveddependency vector without comparing the generated first UB and thegenerated second UB.